1. Field of the Invention
The present invention concerns a fuel cell, and more particularly polymer electrolyte fuel cell, for excluding condensate water generated in a cell body, and preventing flooding due to an excessive humidification of an electrode.
2. Detailed Description of the Prior Art
A solid polymer type fuel cell is formed, as schematically shown in FIG. 7, by laminating a plurality of basic unit I composed by pinching a cell H where a fuel electrode B (anode) is disposed on one of faces of an electrolyte membrane A (solid polymer electrolyte membrane) and an air electrode C (cathode) on the other face respectively, by a separator J where a fuel gas flowing passage D is formed on the fuel electrode side, and an oxidant gas flowing passage F on the air electrode side (3 cells are stacked in FIG. 7). For instance, a plate E where only the fuel gas flowing passage D is formed and a plate G where only the oxidant flowing passage F is formed, are disposed respectively on both sides of a stacked body of this fuel cell.
In the aforementioned polymer electrolyte fuel cell, the fuel electrode side passage D is supplied with a fuel gas (normally, a reformed gas made by reforming a raw fuel into a hydrogen rich gas by a reformer) and, at the same time, the air electrode side passage F is supplied with an oxidant gas (normally, air), electricity is generated by the occurrence of electrochemical reaction through the electrolyte membrane A, and generated water is simultaneously. In short, the fuel cell can generate electricity through the electrochemical reaction between hydrogen gas in the reformed gas and oxygen gas in the air. A reaction for separating a hydrogen molecular into hydrogen ions (proton) and electrons occurs at the fuel cell B while a reaction for generating water from oxygen, hydrogen ion and electron occurs at the air electrode C respectively, the load is supplied with electricity by electrons moving through an external circuit from the fuel electrode B to the air electrode C and, at the same time, water is generated on the air electrode C side.
Fuel electrode: H2→2H++2e−
Air electrode: 4H++O2+4e−→2H2O
Whole: 2H2+O2→2H2O
For the aforementioned polymer electrolyte fuel cell, in case where the electrolyte membrane A is not wet, it does not function satisfactorily as proton electric conductor; therefore, the fuel gas or oxidant gas is humidified, and supplied to the fuel cell body as wet fuel gas or wet oxidant gas, and the electrolyte membrane A is held wet appropriately with moisture continued in these gases. However, in the step of flowing wet oxidant gas through the passage F, water generated on the air electrode C is added in the form of water vapor, making the moisture excessive as it progresses in the passage F, and especially in the downstream side from the middle, it becomes supersaturated and the moisture will be condensed. If this condensate water deposits on the surface of the passage F, and a part of the passage F comes to be clogged, biasing the oxidant gas flow distribution in the passage F, the supply of oxidizing agent gas will locally be clogged, deteriorating the power generation performance. Such clogging of the passage by condensate water may also be provoked in the fuel electrode B side passage D by the back diffusion of generated water.
As a means for resolving this problem, for instance, Japanese Patent Laid-Open No. 1994-89730 discloses a technology for installing a condensate water elimination means comprising a non-humidified oxidant supply unit and a water absorbing material in the middle of the oxidant gas passage. In this case, a dry oxidant gas supplied from the condensate water elimination means is added to the wet oxidant gas from the upstream side thereof, thereby the water vapor partial pressure in the downstream oxidant gas is lowered, and the supersaturated state of the oxidant gas is resolved, the evaporation of condensate water is facilitated and, at the same time, the water absorbing material absorbs condensate water condensed on the inner wall surface of the passage in contact with the upstream side of the non-humidified oxidant supply unit to prevent the passage from clogging. However, according to the aforementioned example, it is necessary to dispose the non-humidified oxidant supply unit and the water absorbing material in the middle of the oxidant gas passage of the separator and to form two oxidant gas passages, humidified and non-humidified, making the structure complicated and the processing difficult. In addition, the control was difficult, because the non-humidified gas cannot be supplied without pressure difference, flow rate and pressure depend on the power generation conditions, or gas distribution in the passage can be disturbed.
Therefore, it is an object of the present invention to supply a polymer electrolyte fuel cell capable of eliminating condensate water, and preventing flooding due to an excessively humidified electrode by a simple structure and easy processing composition.